Many risks, few rewards in warming debate

The fifth report of the Intergovernmental Panel on Climate Change (IPCC) has provided undeniable proof of a remarkable phenomenon: a public debate even more bitter and polarized than the budget showdown.

The intersection of science and policy, of climate and politics, has become a bloody crossroads. Blog-based arguments over ocean temperatures and the thickness of the Greenland ice sheet are as shrill and personal as any Tea Party primary challenge. And the IPCC report -- designed to describe areas of scientific consensus -- has become an occasion for polarization.

Environmental advocates have done their side no favors. The most eager have been caught in a sleight of hand. In the past, they have used relatively brief periods of warming and short-term weather patterns to bolster their arguments about climate disruption -- a tactic that has come back to bite them in the El Nino. Recent warming has been slower than the long-term trend -- what has been called a "pause" or "hiatus." Time scales that environmental advocates once touted as significant are now dismissed as irrelevant. Skeptics have cried gotcha.

In fact, the 15-year warming hiatus is both misleading and pretty much irrelevant. Short-term trends can be exaggerated by the choice of a statistical starting point. The year 1998 was particularly hot. A graph beginning in 2000, for example, would yield a different slope. And the occasional flattening of temperature rises is exactly what you'd expect in climate science, which assumes bumps upward and downward along a generally rising curve. The theory allows for natural variability in a complex system while asserting long-term, upward pressure on temperatures.

However the IPCC report is used or abused, it represents a consensus and not a conspiracy. "Each of the last three decades," it concludes, "has been successively warmer at the Earth's surface than any preceding decade since 1850." The oceans have warmed and grown more acidic. Ice sheets are losing mass. Sea ice and snow cover in the Northern Hemisphere are shrinking. Ocean levels are rising. (Compared to its report six years ago, the IPCC has raised its projection of sea-level rise during this century by about 40 percent.) All these things are plausibly related to increased atmospheric concentrations of greenhouse gases produced in vast amounts by humans. And these trends involve serious public risks.

The report is filled with admissions of uncertainty, which are sometimes seized on as vulnerabilities. Uncertainty is, in fact, essential to the scientific enterprise, which is designed for self-correction. The evidence for human-caused climate disruption is increasingly clear. The magnitude of future disruption is a matter of scientific debate. But when the stakes are high, uncertainty is not a good justification for complacency. Which explains the existence of the insurance industry.

The main problem in dealing with climate change is not scientific uncertainty. It is the inability of political systems to deal with a certain type of risk and reward.

First, in this case, the geographic distribution of risk is unequal. Southern England might eventually have the growing seasons of France. Parts of Africa might see advancing deserts and increasing drought. And while New York City and Bangladesh might both be vulnerable to rising sea levels, only one will have the resources and infrastructure to adapt to change. Urgency will vary by region.

Second, the temporal distribution of rewards is unfavorable. Resources expended today will get only limited results well into the future. Because the cumulative production of carbon is the problem, many of the changes we are seeing are essentially irrevocable. "Most aspects of climate change," says the IPCC report, "will persist for many centuries even if emissions of CO2 are stopped."

This does not mean that restricting greenhouse gas emissions is useless, just that it is politically thankless. Inaction may have terrible results. Even vigorous action, however, would only start limiting the terrible results at some point in the middle of the century. And it would never undo them. We could leave most of the vast reserves of fossil fuels in the ground -- a political and economic impossibility -- and still the ice would melt and the sea would rise. It is no wonder that politicians -- even politicians who believe in warming -- tend to have other priorities.

This leads to a fully justified form of skepticism, not about a scientific consensus but about the ability of political institutions -- incapable of dealing with current crises or predictable fiscal challenges -- to respond prudently to scientific risk when there is little political reward.

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